1. Field of the Invention
The present invention relates to an inverter apparatus in which a three-phase inverter main circuit having a plurality of arms includes a plurality of semiconductor chips for electric power and a driving circuit and a control circuit are provided, particularly relates to the small inverter apparatus having good cooling efficiency and high reliability for an electric automobile, and a method of manufacturing the same.
2. Description of the Related Art
In the electric automobile, miniaturization and the high reliability of the inverter apparatus are demanded, The inverter apparatus having the good cooling efficiency is required in order to realize the miniaturization and the high reliability of the inverter apparatus.
A structure of a conventional inverter apparatus will be described below referring to FIG. 1 to FIG. 3. FIG. 1 is a sectional plan view of the conventional inverter apparatus, FIG. 2 is a sectional side view of the conventional inverter apparatus, and FIG. 3 is a partially sectional view of an inside of the conventional inverter apparatus.
In FIG. 1 and FIG. 2, the inverter apparatus includes a semiconductor device portion 2 for electric power in which a semiconductor chip constituting a three-phase inverter main circuit is mounted, an aluminum electrolytic capacitor 4 which is a smoothing capacitor for an electric source fixed on a fixing base 5, current detectors 101 and 102 which detect current of three-phase output conductors 91 to 93, and a control unit 11, the inverter apparatus is fixed on a bottom surface of a inverter apparatus casing 1 by mounting screws 3.
The semiconductor device portion 2 and the aluminum electrolytic capacitor 4 are electrically connected by a conductor of positive side 7, a conductor of negative side 8, and connecting screws 6. An inlet 12, an outlet 13, and a channel 15 of coolant 14 are provided on the bottom surface of the inverter apparatus casing 1. The semiconductor device portion 2 is cooled by the coolant 14 which enters at the inlet 12 and flows through the channel 15, the coolant 14 goes out from the outlet 13. The coolant 14 is, for example, an anti-freeze solution.
In the semiconductor device portion 2, as shown in FIG. 3, an insulating substrate 17 is laminated and bonded to an upper portion of a metal plate for heat dissipation 16 mounted on the inverter apparatus casing 1, a metal electrode 18 is laminated and bonded to an upper portion of the insulating substrate 17, and an IGBT 191 and a diode 201 of the semiconductor chip are stacked and bonded to an upper portion of the metal electrode 18. The IGBT 191 and the diode 201, the metal electrode 18, and the insulating substrate 17 are contained by an insulative resin package, the metal plate for heat dissipation 16 is adhered to the resin package at an end portion of the metal plate for heat dissipation 16. An inside of the resin package is filled with an insulating gel.
In the semiconductor device portion 2, a thermal conductivity grease 21 is applied to a rear face of the metal plate for heat dissipation 16 in order to reduce contact thermal resistance, the semiconductor device portion 2 is fixed on the bottom surface of the inverter apparatus casing 1, in which the channel 15 is provided, by the mounting screws 3.
In the semiconductor device portion for electric power 2 having the above-described configuration, when the IGBT 191 and the diode 201 of the semiconductor chip are conducted, loss is generated. Since the insulating gel of a heat insulator is filled in upper potions of the IGBT 191 and the diode 201, almost part of the loss generated in the IGBT 191 and the diode 201 is thermally conducted to the lower metal electrode 18. The loss thermally conducted to the metal electrode 18 is thermally conducted to the metal plate for heat dissipation 16 through the insulating substrate 17. As shown in FIG. 1 to FIG. 3, the metal plate for heat dissipation 16 is pressurized and contacted by the mounting screws 3 to the bottom surface of the inverter apparatus casing 1, the loss is dissipated by the coolant 14.
In the above-described conventional inverter apparatus, there are problems as follows.
A first problem is that the thermal conductivity grease 21 is applied to the rear face of the metal plate for heat dissipation 16 in order to reduce the contact thermal resistance, the metal plate for heat dissipation 16 is pressurized and contacted to the bottom surface of the inverter apparatus casing 1 in which the channel 15 is provided by the mounting screws 3 disposed about a periphery of the semiconductor device portion 2, so that an applied pressure is not uniformly applied to the whole metal plate for heat dissipation 16.
For this reason, the contact thermal resistance between the metal plate for heat dissipation 16 and the inverter apparatus casing 1 becomes as quite large as thermal resistance of an inside of the semiconductor device portion 2, which results in the bad cooling efficiency.
In addition to the first problem, a second problem is that the thermal conductivity grease 21 applied to the rear face of the metal plate for heat dissipation 16 might deteriorate on a long-term basis, which causes reliability to be decreased.
These problems can not finally contribute to improvement of current-carrying capacity of the inverter apparatus, furthermore, the above-described problems generates another problem that the inverter apparatus increases in size as a cooler and the like increase in size and it is difficult that the reliability is not secured presupposing a long-term service of the inverter apparatus.